This study attempted to determine which combination of plaque or saliva, and tryptic soy agar, bacitracin (TSY20B) or mitis salivarius, bacitracin media, yielded the highest caries-predictive values for mutans counts in children with different caries prevalence. Sixty children were divided into three equally sized groups: caries free, low caries and high caries. Eighteen months later, their caries incidence and initial mutans count were compared. Fissure plaque on TSY20B yielded a high correlation between mutans counts and caries prevalence (P<0.009, r=3346) and incidence (P<0.003, r=4521). The caries-predictive values obtained demonstrate that the coefficient of variation of mutans counts from lower first-molar fissure plaque on TSY20B accounts for 20.4% of the variation in final caries index. This strong correlation provides a valuable tool for the identification of caries-prone individuals.